Personal and environmental characteristics related to epithelial ovarian cancer. I. Reproductive and menstrual events and oral contraceptive use.

In two case-control studies conducted in the six-county San Francisco Bay Area, 111 women diagnosed with epithelial ovarian carcinoma in 1974-1977 and 188 women diagnosed in 1983-1985 were interviewed concerning their menstrual, sexual, and reproductive histories. For comparison, interviews were conducted with 752 control women admitted to the same hospitals within six months of the cases; for cases diagnosed in the later period, interviews were also conducted with an additional 259 population-based controls selected by random digit dialing. Controls were matched to cases by age and race. Qualitative and quantitative findings were similar for the two studies. In the combined data, cases were more likely than their matched controls to have been nulliparous, to have undergone menarche at an early age, and to have refrained from using oral contraceptives. Menopause occurred slightly later for cases than for controls, but the differences were not statistically significant. Neither age at first term pregnancy (20 or more weeks gestation) nor number of term pregnancies was predictive of ovarian cancer risk. The protection afforded by oral contraceptive use was independent of parity, and it increased with increasing duration of use. There were no trends in risk with time since last oral contraceptive use or with time since first use, after adjustment for duration of use. These observations suggest that oral contraceptive use decreases risk for ovarian cancer, rather than merely indicates fertility, which may itself decrease risk of developing the disease. The authors combined reproductive characteristics and oral contraceptive use to estimate a woman's total duration of ovulation, which was positively associated with ovarian cancer risk (p less than 0.001 for trend). These observations support the concept that the greater the duration of ovulation or accompanying endocrinologic phenomena, the greater a woman's risk for ovarian cancer.